The present invention relates to a drill having increased rigidity and adapted to drill holes, especially deep holes, with an improved cutting efficiency.
Conventional drills are formed with helical flutes in the outer periphery of the shank for discharging chips. Such flutes have a width ratio of as large as about 1, so that the shank is low in torsional rigidity and in bending rigidity. Consequently, the drill is unable to cut workpieces efficiently especially for forming deep holes. Further, since the shank has low rigidity, the drill fails to form holes having accurate circularity and defined by a surface of low roughness.
Accordingly, an object of the present invention is to provide a drill including a shank of enhanced rigidity and thereby adapted to exhibit improved cutting performance for drilling holes, especially deep holes.
Another object of the invention is to provide a drill having a shank of increased rigidity and permitting smooth discharge of chips.
Another object of the invention is to provide a drill having cutting edges which form chips of reduced width so that the chips can be discharged with decreased resistance.
Still another object of the invention is to provide a drill having chip discharging flutes which are easy to form, the drill being adapted to produce chips which are broken into pieces of suitable length and rendered easy to handle when discharged.
These and other objects and features of the invention will become more apparent from the following description of embodiments given with reference to the accompanying drawings.